Stroke Recovery: Looking beyond physical therapy to electrical stimulation

Strokes occur when blood supply to a part of the brain is blocked by something or when a blood vessel located in the brain bursts. Damage to the brain results from a stroke. Stroke is the second leading cause of death worldwide, following heart disease. It is also the leading cause of disability worldwide. The risk of stroke increases with age. Although about 80% of stroke patients survive, survivors encounter a negative impact on their quality of life. This is due to stroke symptoms that include motor impairments, loss of coordination, and limb hemiparesis. Recovery from stroke can be difficult due to many clinical factors, including the formation of glial scars that prevent axon regeneration. Task-oriented training, such as physical therapy can help with motor rehabilitation, but physical therapy alone is not enough. Electrical stimulation provides a more targeted approach to motor rehabilitation and may produce better results. Electrical stimulation can cause changes in neuroplasticity, effectively rewiring the brain and improving motor capability. 

The review article, Rewiring the Lesioned Brain: Electrical Stimulation for Post-Stroke Motor Restoration, by Bao et al., gives an overview of current electric stimulation methods and their mechanisms and discusses the future of electrical stimulation concerning stroke recovery. The article describes two categories of electrical stimulation: noninvasive brain stimulation (NIBS) and peripheral electrical stimulation. NIBS is often used as a supplementary tool in stroke recovery. It continues to modulate brain plasticity even after the stimulation period. This can further enhance the motor function of affected limbs. NIBS includes transcranial direct current stimulation (tDCS), transcranial magnetic stimulation (TMS), and cerebellum and spinal cord stimulation. Peripheral electrical stimulation has also shown promise regarding stroke recovery. The two forms of peripheral electrical stimulation discussed in the article were neuromuscular electrical stimulation (NMES) and transcutaneous electrical nerve stimulation (TENS). Although stroke patients cannot voluntarily move limbs affected by the stroke, their spinal motor neurons are intact and can be excited by NMES. NMES can modulate neuron hyperpolarization and depolarization and excite peripheral nerves. The article also discusses other forms of invasive electrical stimulation that have emerged recently, but need to be studied further. Deep brain stimulation, which stimulates electrodes that are implanted in deep regions of the brain, can stimulate impaired neural circuits, facilitating reorganization and improving plasticity. 

Investigating one of the two categories of electrical stimulation discussed in the review article, Chen et al.’s Effects of 8-week sensory electrical stimulation combined with motor training on EEG-EMG coherence and motor function in individuals with stroke utilizes peripheral electrical stimulation to study its effects on chronic stroke patients’ neuromuscular control and hand function. The study involved twelve subjects who were either assigned to the control group or received electrical stimulation. The groups received twenty minutes of hand function training twice a week, and the subjects that were not part of the control group also received 40-minute sessions of electrical stimulation before each biweekly training session. The subjects were assessed before the experiment, on the fourth and eighth week of the experiment, and four weeks after the conclusion of the experiment, as a follow-up. Subjects who received electrical stimulation showed significant improvement in corticomuscular control at the four-week mark compared to subjects who received sham electrical stimulation. The article mentioned that recovery for patients afflicted with chronic stroke was more difficult than that of patients with a more recent stroke. However, this study was able to show improvement in corticomuscular control even in chronic stroke patients.

Although the exact mechanisms of stroke recovery through electrical stimulation are not completely understood yet, it has shown much promise in future treatments. In conjunction with physical therapy, much improvement can be observed. With further research into the newer methods mentioned in Bao’s review article and the peripheral electrical stimulation investigated in Chen’s experiment, stroke recovery can be made more efficient and effective. Together, the two articles show the potential of electrical stimulation for stroke survivors and point toward further research.

References:

1.  Bao S. Rewiring the Lesioned Brain: Electrical Stimulation for Post-Stroke Motor Restoration

J Stroke. 2020 Jan 31. doi: https://doi.org/10.5853/jos.2019.03027.  
2. Pan LH, Yang WW, Kao CL, Tsai MW, Wei SH, Fregni F, Chen VC, Chou LW. Effects of 8-week sensory electrical stimulation combined with motor training on EEG-EMG coherence and motor function in individuals with stroke. Sci Rep. 2018 Jun 15;8(1):9217. doi: 10.1038/s41598-018-27553-4.

The Neuroscience Behind Binge-Eating

 The Neuroscience Behind Binge-Eating

Binge-eating is the most common eating disorder and affected over 2.8 million of Americans in 2016. (1) In the words of the National Eating Disorder organization, binge-eating is “characterized by recurrent episodes of eating large quantities of food; a feeling of a loss of control [...], experiencing shame, distress, or guilt afterwards.” People affected by this disorder will often use unhealthy compensatory actions like purging or consuming laxatives. In this blog post, we will study the neuroscience and neuroanatomy of binge-eating through the article Neurobiology of Binge-Eating Disorder – A Synopsis by Dr. Sanil Rege (2). and drawing parallels to the research paper Reduce caloric intake allows access-induced consumption differences to emerge with concentrated sucrose level by Dr. Milan D Valyear (3). 

In the article Neurobiology of Binge-Eating Disorder – A synopsis, Dr. Sanil Rege discusses the negative physical and mental health consequences of Binge-Eating Disorder (BED). The disorder is fueled by impulsivity and compulsivity, controlled by the prefrontal cortex and striatum. In terms of impulsivity, people affected by BED have a higher impulsivity score (according to Barrat BIS-11 and UPPS impulsivity scales) than obese or normal weight people. The ventral striatum, linked to the thalamus, ventromedial prefrontal cortex (VMPF) and the anterior cingulate cortex (ACC) are all involved in the neurobiological pathway of impulsivity. In terms of compulsivity, the repetitive behavior of eating is related to the dorsal striatum, thalamus and the orbitofrontal cortex. In addition to impaired impulsive and compulsive behaviors, patients with BED are more prone to alterations in reward system, with dysregulated appetite-regulating hormones, impaired decision-making behavior and other cognitive deficits. Indeed, the reward circuitry, mediated by dopaminergic pathways is dysregulated in patients with BED.

  The research paper Reduce caloric intake allows access-induced consumption differences to emerge with concentrated sucrose level by Dr. Milan D Valyear and Dr. Roelof Eikelboom studies the differences in caloric intake between intermittent fasting and continuous feeding and how sucrose concentration can affect these intakes. Through three experiments, Dr. Valyear was able to show that access-induced consumption differences were dependent on the duration of the fasting and the concentration of sucrose. In a first experiment, Dr. Valyear studied the impact continuous feeding and intermittent fasting has on caloric intake with low concentration sucrose (4%). In a second experiment, conditions were similar except for sucrose concentration (8%), as well as adding bitter quinine (0.005%) to the sucrose. Finally, in a third experiment, the rats were divided in four groups and were given 8% sucrose concentration with different amounts of quinine (0.0025%, 0.005%, 0.01%, and 0.02%). Results of this experiment proved the complex relationship between taste (bitterness of quinine), caloric intake, fasting, fasting durations.

Both articles provide insight on the neurobiology of different eating habits. In the Neurobiology of Binge-Eating Disorder article by dr. Rege we gain a better understanding of which parts of the brain are impaired in patients with BED. Individuals affected by this disorder will have an unhealthy relationship with food. Similarly, in the research paper by Dr. Valyear studies how different factors, like fasting or sucrose concentration, affect caloric intake in rodents. The study focuses on the relationship between eating behavior, caloric intake, fasting, and taste. Even though the two articles focus on different types of eating behavior, they both offer valuable and intricate insight on the neurobiology behind eating behaviors. 

References

1. Schaeffer, J. (2016, December 19). Binge Eating Disorder Statistics: Know the Facts. Healthline. https://www.healthline.com/health/eating-disorders/binge-eating-disorder-statistics

2. Rege, S. (2022, February 7). Neurobiology of Binge Eating Disorder - A Synopsis. Psych Scene Hub. https://psychscenehub.com/psychinsights/neurobiology-of-binge-eating-disorder/

3. Valyear, M. D., & Eikelboom, R. (2021). Reduced caloric intake allows access-induced consumption differences to emerge with concentrated sucrose solutions. Physiology & Behavior, 234, 113388. https://doi.org/10.1016/j.physbeh.2021.113388

Autism Spectrum Disorder (ASD) Assessments

    Autism Spectrum Disorder (ASD) has no distinct cause. It is a developmental disorder that has causes linked to genetics, biology, and even living environments (CDC). There are different signs that can help a parent identify ASD in their child, but the most common early signs are avoidance of eye contact and lack of recognition when someone is speaking to them. When looking at trends in people with ASD it can be seen that the disorder is more common in men than woman, hinting that there may be a factor in the development of ASD that is genetic. In addition, the CDC noted that people with certain genetic disorders such as fragile X syndrome, tuberous sclerosis, and down syndrome are more likely to have ASD. It is important to note that genetic testing can not alone diagnose ASD, it rather can find possible genetic causes of ASD. 

    Maggie Guy's article Cortical Source Analysis of the Face Sensitive N290 ERP Component in Infants at High Risk for Autism investigated the components of potential indicators in infants who are at risk for ASD. During the team's experimentation, it was noted how important it is to use group-specific head models in order to produce the most accurate results. A finding that stemmed from this project was that the IBIS model turned out to be the most consistent and overall better choice than the study-specific or group-specific models. The study used methods of cortical source analysis to study N290 event-related potentials (ERP). Guy's team studied the ERP reactivity in children with varying risks of having ASD, specifically looking into the magnitude of responses when the children were presented with faces or toys. It was found that the children had a greater ERP response when presented with faces rather than toys. Guy's work on studying face sensitive N290 ERPs implies that there still is much to discover regarding early ASD indicators when studying children at varying risks for ASD.

    A study titled Autism screening tests: A narrative issue that features researchers
Fatemeh Fekar Gharamaleki and Boshra Bahrami analyzed 19 different Autism screening assessments. As mentioned in the article, ASD symptoms are present even as early as within the first two years of a child's life (Journal of Public Health Research). By evaluating various screening assessments the team was able to learn the strengths and weaknesses of each type of testing, as well as gain insight into which method of testing is most efficient for different children. The team investigated different forms of assessments: 1 confrontation game, 8 checklists, and 10 questionnaires. Because the goal of the research was to gather data regarding different screening assessments to ultimately help therapists select the most relevant form for their patients, the study focused primarily on the components to each assessment and the demographic that each of the 19 assessments were intended for. 

    The two studies share a common topic relating to ASD and different methods you can take to identify ASD in children. Guy's study focus on ERP responses in children offers a potential biological indicator of ASD, while Gharamaleki's study conveys various methods of screening in children who may be suspected to have ASD. Both approaches indicate a possibility of narrowing down ASD diagnoses in children. Results such as these are important when therapists and doctors move forward in diagnosis and treatment. Screening assessments and cortical source analysis are two methods of detecting ASD or ASD related symptoms in children, and when used together can potentially solidify the diagnostic or treatment plans of therapists, psychiatrists, and doctors. 

Sources:

“Autism Spectrum Disorder, Family Health History, and Genetics.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 18 May 2022, https://www.cdc.gov/genomics/disease/autism.htm.

“Genetic Testing for Autism.” Autism Speaks, https://www.autismspeaks.org/expert-opinion/should-i-or-we-have-genetic-testing-autism.

Gharamaleki, Fatemeh Fekar, et al. “Autism Screening Tests: A Narrative Review .” Sage Journals, 16 May 2022, https://journals.sagepub.com/doi/10.4081/jphr.2021.2308.

Guy, Maggie W., et al. “Cortical Source Analysis of the Face Sensitive N290 ERP Component in Infants at High Risk for Autism.” MDPI, Multidisciplinary Digital Publishing Institute, 25 Aug. 2022, https://www.mdpi.com/2076-3425/12/9/1129.

The Default Mode Network and PTSD

Posttraumatic Stress Disorder can be a debilitating disorder to live with, characterized in part by hypervigilance and reduced filtering of sensory input to the brain. Research has been focused on how treatment can center on regions of the brain involved in PTSD to improve symptoms in those with the disorder. 

In the research article entitled "Posttraumatic Stress Disorder Is Associated with a Dysrhythmia across the Visual Cortex and the Default Mode Network," Clancy et. al. hypothesized that there is an association between a decrease in alpha activity and the ability to filter out sensory input in the default mode network. The DMN is principally involved in the activity of the resting brain, with alpha activity being the resting brain's dominant electrical component. The researchers found deficits in alpha activity in participants with PTSD, correlating with symptoms of hypervigilance. This decreased activity is associated with lessened visual cortical inhibition, contributing to the lack of filtering sensory input. These findings support the targeting of alpha stimulation in the visual-cortex-DMN system in treatment of PTSD.

Another instance of PTSD and DMN correlation is explored in the article “Default mode network abnormalities in posttraumatic stress disorder: A novel network-restricted topology approach.” The default mode network comprises many other areas, including the ventromedial and dorsomedial prefrontal cortices and the posterior cingulate cortex. It is a main network in the area of intrinsic connectivity networks (ICNs), or areas that couple to serve spatial functions. The article details the importance of developing studies to research ICN involvement in psychiatric disorders. This study sought to explore connectivity in the DMN, specifically in its involvement with PTSD. They hypothesized that PTSD symptoms are associated with decreased functional connectivity in the DMN. Using neuroimaging and anatomical connectivity, the researchers studied symptoms in veterans and found reduced DMN connectivity in those with high severity of symptoms. 

Both articles focused on the region of the brain involved with resting activity, the default mode network. While the first article centered on correlation of alpha activity with symptoms, the second focused on functional connectivity in the region in association with symptoms. In both studies, results indicated a lower connectivity and function in the DMN. This contributes to the hypervigilance and general anxiety associated with PTSD. When an individual's general resting state is disturbed, anxiety and stress can emerge, disrupting the quality of life. The importance of developing proper and region-specific treatment of PTSD symptoms is heavily stressed in both articles. There are many different ways to target these integral regions to lessen stress and hypervigilance.

References: 

1. Teddy J. Akiki, Christopher L. Averill, Kristen M. Wrocklage, J. Cobb Scott, Lynnette A. Averill, Brian Schweinsburg, Aaron Alexander-Bloch, Brenda Martini, Steven M. Southwick, John H. Krystal, Chadi G. Abdallah, Default mode network abnormalities in posttraumatic stress disorder: A novel network-restricted topology approach, NeuroImage, Volume 176, 2018, Pages 489-498, ISSN 1053-8119, https://doi.org/10.1016/j.neuroimage.2018.05.005.

2. Kevin J. Clancy, Jeremy A. Andrzejewski, Jessica Simon, Mingzhou Ding, Norman B. Schmidt and Wen Li, Posttraumatic Stress Disorder Is Associated with α Dysrhythmia across the Visual Cortex and the Default Mode Network, eNeuro 20 July 2020, 7 (4) ENEURO.0053-20.2020; DOI: https://doi.org/10.1523/ENEURO.0053-20.2020

Alzheimer’s Disease

In the study of neuroscience and neurobiology, the most common disease that is brought up is Alzheimer’s disease. Is a neurodegenerative disease that affects the uptake of new memories with difficulty in learning. The disease affects around 3 million Americans every year with a majority of the people that are effective are over the age of 80. Alzheimer’s disease can be broken down into 2 different schools of thought the first being sporadic Alzheimer this campuses around 90-95 % of cases. Sporadic Alzheimers is primarily due to environmental and genetic factors as we grow older a gene known as APOE-5 tends to be less effective causing a decrease in the controlled response of protein amyloid (APP). As this protein is thought to help in nerve growth and repair after an injury. The second school of thought of Alzheimer’s is known as Fimial Alzheimer’s this is a rare form of Alzheimer’s as it occurs earlier in life around the age of 40. This is caused by the PSEN-1 and the PSEN-2 gene and is commonly tied up with Down syndrome as PSEN genes translate for an extra copy of the APP protein this is dangerous because an increase in the cleavage of the Amyloid beta protein creates more plack that can disrupt nero chemical synapses. 

The symptoms of Alzheimer’s disease can differ between classes of patients but the most common symptom is dementia. This is caused by the build-up of the APP protein although this protein is used for repair of the neron after long-term use it begins to degrade and needs to be cleaved. But over time due to the biochemical properties of APP, the molecule tend to clump up together creating neurochemical plaques. This will then disrupt the synaptic signaling of the neuron and prevent the uptake of key nutrients needed for cellular function. This will in turn cause cell death of neurons over a period of time the cells will begin to shrink brain size and connections. This is devastating for patients health as they start to lose small memories at first but as the disease progress, it will impact problem-solving skills and short-term memories. An example of the early stages of symptoms is when a person has difficulty creating and following a plan or working with numbers. This can manifest in being unable to track dates or messaging a budget, even forgetting their car keys in the vehicle. The second stage of the disease can be confusing and understanding significant events. An example of this is forgetting a conversation that just transpired or misplacing items. Another symptom that can occur in the second stage is the inability to understand relationships, balance, or read. As some patients have reported having trouble with vocabulary an example may be saying a watch is a hand clock. The third stage of Alzheimer’s disease is known to be an extreme form of dementia this is when people forget their close family members like a parent or a spouse. This is attributed to a decrease in brain size as it tries to preserve its structure inorder to maintain boldly function to say alive.  But there are ways to prevent Alzhemier’s disease by maintaing a health life style like being physicaly active,eating nutritious food and geting 8 hours of sleep. By taking epigenetic actions we are able to combat Alzhemiers disease as takeing action early by visiting a clinical professional can also prevent or decreass the saverity of symtoms for Alzhemiers disease.

Work cited: 

CDC, CDC. “Reducing Risk of Alzheimer's Disease.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 13 Sept. 2022, https://www.cdc.gov/aging/publications/features/reducing-risk-of-alzheimers-disease/index.htm. 

Association, Alzheimer's. “10 Early Signs and Symptoms of Alzheimer's.” Alzheimer's Disease and Dementia, 2023, https://www.alz.org/alzheimers-dementia/10_signs. 

Elsevier, Osmosis, director. Alzheimer's Disease - Plaques, Tangles, Causes, Symptoms & Pathology. YouTube, 22 Mar. 2016, https://youtu.be/v5gdH_Hydes. Accessed 30 Apr. 2023. 

Transcranial Direct Current Stimulation and Memory Enhancement

     Transcranial direct current stimulation (tDCS) is a brain stimulation method that uses low direct current via electrodes on the head. Currently, many researchers are investigating the potential of tDCS in many different conditions. tDCS has many advantages as it is non-invasive, it does not pose health risks, and it is cost effective (Bjekić et al., 2021). However, there is an ongoing debate on whether or not tDCS modulates brain activity enough to positively impact patients with neurological disorders (Vanneste et al., 2020). Recently, neuroscientists have been researching the effects of tDCS on memory enhancement. Vanneste el al. researched the effect of tDCS on the brain circuits involved in memory. Bjekić et al. further discusses how tDCS can be used for memory enhancement.

Venneste et al. researched tDCS in relation to its effects on locus coeruleus–noradrenergic (LC-NAc) system and communication between the LC, amygdala, and hippocampus and the lasting effects of memory. In a resting state fMRI experiment, researchers found an increased correlation strength between LC and the right hippocampus (Vanneste et al., 2020). The right hippocampus has been known to play a crucial role in spatial memory. Furthermore, Venneste et al. further discussed tDCS in relation to memory. Researchers gave participants a face-name association memory task. Then, participants were given ON-tDCS during the encoding and consolidation phase of memory. ON-tDCS is occipital nerve transcranial direct current stimulation. The occipital nerve can aid memory as the ascending fibers of the occipital nerve link to the locus coeruleus, which promotes noradrenaline release. The noradrenergic pathway drives hippocampal activity, as it modifies functional connectivity and supports the consolidation of memory (Vanneste et al., 2020). Venneste et al. found that participants were able to recognize more faces from the face-name association memory task after ON-tDCS. These findings show that ON-tDCS positively impacts memory consolidation. 

Bjekić et al. also studied the effects of tDCS on memory enhancement. Bjekić et al.used a weak constant anodal current in order to stimulate targets within the cortico-hippocampal functional network that are engaged in memory processes. Bjekić et al. specifically researched the effects of tDCS on associative memory and working memory using oscillatory tDCS, which mimics “a natural brain rhythm to promote hippocampus-dependent memory functions” (Bjekić et al., 2021). Bjekić et al.’s results show that after 20 minutes of right frontal tDCS, working memory was enhanced. Both verbal and spatial working memory were enhanced. However, when left frontal tDCS was applied, no significant difference in working memory was seen. Furthermore, Bjekić et al.’s results on associative memory further demonstrate the results found by Venneste et al. Bjekić et al. found that after 20 minutes of tDCS on the left posterior parietal cortex, memory for face-word associations were improved.

In conclusion, research done by Venneste et al. and Bjekić et al. emphasize the positive impact that tDCS can have on memory. With this research, more research can be done using tDCS to further understand its impact on memory. Further research may look at the implications of using tDCS as preventative therapy for those at risk for Alzhiemer’s or dementia.

References

Bjekić, J., Živanović, M., Filipović, S. R. Transcranial Direct Current Stimulation (tDCS) for Memory Enhancement. J. Vis. Exp. (175), e62681, doi:10.3791/62681 (2021).

Sven Vanneste, et al.,The peripheral effect of direct current stimulation on brain circuits involving memory. Sci. Adv. 6, eaax9538 (2020). DOI:10.1126/sciadv.aax9538

Strokes and Recovery

    According to the CDC, every year, more than 795,000 people suffer from a stroke in the United States. A stroke is known as a transient ischemic attack which means that blood flow to the brain is blocked. Without any blood flowing, the brain cannot receive oxygen nor nutrients. This then leads to cells dying which can furthermore lead to brain damage. There are many reasons that a person can experience a stroke, some of them include, high blood pressure, high cholesterol, smoking, obesity, diabetes, etc.  An individual who has suffered from a stroke can come out with many complications.  Some include difficulty speaking, loss of bladders and bowel control, loss of bone density or strength, loss of vision, hearing or touch, etc. Due to a stroke being able to cause damage to several brain areas, it is a very serious condition that requires medical attention immediately. 

    In Vincent C-F Chen’s article, “Effects of 8- week sensory electrical stimulation combined with motor training on EEG -EMG coherence and motor function in individuals with stroke”, Chen completed a research where tested how ES (electrical stimulation) can affect motor coordination in a stroke patient. Patients were split into a control and placebo group where both received the intervention of ES twice a week through the course of eight weeks. The study took in people who were chronic stroke survivors with specific criteria that needed to be met. The research was completed after 8 weeks, and a series of results were able to be determined. One key result that was found was the overall effect of ES on the chronic stroke survivors. After the research was completed, the study demonstrated that those who received ES showed improvements in their motor skills. Although limited, motor recovery is still possible in patients. The article explained that chronic stroke patient have a lower chance of motor recovery than patients who suffered from a stroke and received treatment 30 days later. However, with this study, most patients were chronic stroke patients, and still showed improvement with ES treatment.

    In a similar article, research was conducted to give physical therapists evidence-based resource on when they should use NMES (neuromuscular electrical stimulation). In this article, one area that they targeted was NMES with stroke rehabilitation. Similar to Chen’s research, electrical stimulation was used to promote recovery. However, with this article they specifically used NMES and targeted muscle strengthening and recovery of limb function of stroke patients (both acute and chronic stroke). Since this article was intended to give therapists evidence, it also targeted muscoskeletal conditions, critical illnesses, and advanced disease states. This article later goes into detail to give therapists more information. It gives details about specific areas that need the attention, and how to complete the task. For stroke patients, there were four different types of treatments provided, all of which gave evidence of increased motor activity in the patient.

    In comparison to Dr. Chen’s research, this article was more specific. It gave different conditions, and specifics of each condition. In addition, it also used NMES rather than ES. All in all, it has been determined that electrical stimulation can cause improvements with motor function and can be used to help stroke patients recover. With the correct equipment and conditions, electrical stimulation can be used in physical therapy to improve a patient’s conditions after they suffer from a stroke.

References: 

Nussbaum EL, Houghton P, Anthony J, Rennie S, Shay BL, Hoens AM. Neuromuscular electrical stimulation for treatment of Muscle Impairment: Critical Review and recommendations for clinical practice. Physiotherapy Canada. 2017;69(5):1-76. doi:10.3138/ptc.2015-88 

Stroke facts. Centers for Disease Control and Prevention. https://www.cdc.gov/stroke/facts.htm#:~:text=Stroke%20statistics,-In%202020%2C%201&text=Every%20year%2C%20more%20than%20795%2C000,are%20first. Published October 14, 2022. Accessed April 28, 2023. 

Pre- and Perimenopausal Hormone Interventions Can Have Positive Implications in Cognition Later in Life

         In their paper “Perimenopausal use of hormone therapy is associated with enhanced memory and hippocampal function later in life” Pauline M. Maki et al. examined a phenomenon they termed the “critical window hypothesis”, which suggests that hormone therapy (HT) in the perimenopausal (during menopause) state can be beneficial to long-term cognition, whereas hormone therapy during the postmenopausal period shows neither beneficial nor harmful effects (Maki et al., 2011). The researchers were interested in examining patterns of brain activation in the medial temporal lobe, which they hypothesized might play a role in verbal encoding and word recognition. They found that subjects who were given perimenopausal hormone therapy scored better than their perimenopausal non-HT counterparts in both areas and identified that their results were consistent with the “critical window hypothesis” (Maki et al., 2011).   

        In addition to perimenopausal HT, the long-term premenopausal usage of another form of hormone intervention, hormonal contraceptive usage, was hypothesized to have a positive, duration-dependent effect on long-term cognitive function (Egan et al., 2012). It was found that women who utilized hormonal contraceptives showed significantly better performance in both visuo-spatial ability and speed & flexibility compared to matched “never users” who did not take hormonal contraceptives (Egan et al., 2012). Not only was this association determined, but there was also a dose-dependent aspect to this conclusion in which the longer a subject took hormonal contraceptives, the better their cognitive scores were in the aforementioned areas, especially in subjects with fifteen or more years of use (Egan et al., 2012). 

        

        Together, these two studies show the benefits of different hormone interventions on later-year cognition. Notably, these interventions showed benefits after use during different times in the menopausal timeline, with hormonal contraception showing benefits after long-term premenopausal usage and hormone therapy showing cognitive improvements during the perimenopausal window (aligning with the “critical window hypothesis”). This shows that the potential for hormone effects on cognitive health is vast and has promising applications at any point in the reproductive lifespan, and highlights an interesting link between reproductive, endocrine, and neural health. 

References: 

Egan, K. R., & Gleason, C. E. (2012). Longer duration of hormonal contraceptive use predicts 

better cognitive outcomes later in life. Journal of women's health (2002), 21(12), 1259 

`1266. https://doi.org/10.1089/jwh.2012.3522 

Maki, P. M., Dennerstein, L., Clark, M., Guthrie, J., LaMontagne, P., Fornelli, D., Little, D., 

Henderson, V. W., & Resnick, S. M. (2011). Perimenopausal use of hormone therapy is 

associated with enhanced memory and hippocampal function later in life. Brain 

research, 1379, 232–243. https://doi.org/10.1016/j.brainres.2010.11.030